CN108414113B - Fire alarm system and method for predicting optical fiber temperature by using multipoint temperature discrete coefficients - Google Patents
Fire alarm system and method for predicting optical fiber temperature by using multipoint temperature discrete coefficients Download PDFInfo
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Abstract
The invention discloses a fire alarm system and a method for predicting the temperature of an optical fiber by using a multipoint temperature dispersion coefficient.A distributed optical fiber temperature measurement system is used for acquiring the light intensity values of Anti-Stokes light and Stokes light at each point of the optical fiber and the corresponding demodulated temperature value, processing the acquired light intensity and temperature value, and comparing the temperature and light intensity with an alarm threshold value to determine whether a differential temperature or constant temperature alarm condition is met; meanwhile, the temperature at the next moment is predicted by using the current temperature value and the discrete coefficients of the temperatures at a plurality of past points, and whether an alarm is needed or not is judged; if the alarm condition is met, the alarm position is positioned, and the alarm time is displayed. The method introduces a light intensity judgment method in the differential temperature alarm method, thereby effectively reducing the probability of false alarm; in the method for prejudging the temperature of the optical fiber, the temperature change condition at the future moment is predicted by using the discrete coefficients of the current temperature and the past temperature, so that the alarm response time is effectively reduced.
Description
Technical Field
The invention relates to the technical field of temperature detection, in particular to a fire alarm system and a fire alarm method for predicting optical fiber temperature by using multipoint temperature discrete coefficients.
Background
The distributed optical fiber Raman temperature measurement system mainly utilizes the spontaneous Raman scattering principle in optical fibers to measure temperature and uses the optical time domain reflection principle to position, thereby realizing a novel temperature sensing system for measuring a temperature field in real time. Compared with the traditional electronic temperature sensor, the electronic temperature sensor has the inherent characteristics and intrinsic safety of electrical insulation, corrosion resistance, geometric structure variability, wide signal transmission bandwidth, low information long-distance transmission loss and the like. The method is widely applied to detection of oil wells, oil depots and pipelines, seismic survey observation and monitoring of power systems and communication systems.
In the temperature alarm method of the distributed Raman temperature measurement system, the current mainstream alarm method is to set a fixed alarm threshold value when the system is started, and when the temperature of a certain position of an optical fiber measured by the system is higher than the set alarm threshold value, the system starts to alarm. The speed of the alarm mode mainly depends on the acquisition rate of a high-speed acquisition card and the running time of a temperature demodulation program, and if the response alarm time standard of a linear fire detector meeting the national safety standard is reached by the alarm mode, the requirement on system hardware is high, the alarm mode is not economical and the accuracy cannot be guaranteed. In some places with high requirements on temperature early warning, such as underground safety, forest fire prevention, aerospace temperature measurement places and the like, the temperature alarm mode with slow response time and single early warning method cannot achieve safety and accuracy.
Because the existing temperature alarm method for distributed Raman temperature measurement is limited by the acquisition speed of an acquisition card and the like and cannot reach the national safety standard in places needing accurate alarm, a new temperature alarm method with quicker response is urgently needed to meet the temperature measurement requirements of the important places.
In addition, the existing patent document with the application number of "201710095023.9" has the patent name of "intelligent temperature early warning method for raman thermometers", and the algorithm of the used optical fiber temperature prediction program is complex, so that the requirement of timely fire alarm cannot be met.
Disclosure of Invention
In order to solve the defects of the prior art, the invention provides a fire alarm system for predicting the temperature of an optical fiber by using a multipoint temperature dispersion coefficient, and solves the problems that the response time of a temperature alarm method of the conventional distributed optical fiber temperature measurement system is slow and the temperature cannot be predicted accurately and effectively.
A fire alarm system for predicting the temperature of an optical fiber by using multipoint temperature dispersion coefficients comprises: a distributed optical fiber Raman temperature measuring system is provided,
collecting light intensity values of Stokes light and anti-Stokes light of each point of the optical fiber and corresponding demodulated temperature values through a distributed optical fiber temperature measuring system, processing the collected light intensity and temperature values, and comparing the temperature and light intensity with an alarm threshold value to determine whether a differential temperature or constant temperature alarm condition is met; meanwhile, the temperature at the next moment is predicted by using the current temperature value and the discrete coefficients of the temperatures at a plurality of past points;
during temperature prediction, the current time T of the same position of the optical fiber is measured and recorded in continuous timenThe previous setting of the secondary temperature data, the current time TnDividing the previously set secondary temperature data into three groups according to the time sequence, averaging the temperature data of each group, if the absolute value of the difference between the temperature average value of the third group and the temperature average value of the second group is larger than the absolute value of the difference between the temperature average value of the third group and the temperature average value of the second group, performing second temperature prediction alarm, otherwise, setting a threshold value of the difference of discrete coefficients, and calculating the current time TnIf the absolute value of the difference between the multipoint temperature discrete coefficient at the current moment and the multipoint temperature discrete coefficient at the previous moment in the previously set secondary temperature data is greater than the threshold value of the set discrete coefficient difference, a first temperature prediction alarm is carried out.
Furthermore, the distributed fiber Raman temperature measurement system comprises a pulse laser, wherein pulse light emitted by the pulse laser enters the reference fiber through the wavelength division multiplexer and then enters the sensing fiber through the optical switch;
the middle part of each sensing optical fiber is respectively and randomly selected to be used as a first reference optical fiber and a second reference optical fiber with a certain length, and the two optical fibers are respectively placed in the respective corresponding constant-temperature water bath equipment.
Furthermore, the pulse light generates backward scattering light at each point inside the reference optical fiber and the sensing optical fiber, wherein the backward stokes light and the backward anti-stokes light enter the photoelectric detector through two output ends of the wavelength division multiplexer, then the light intensity curves of the stokes light and the anti-stokes light are obtained through the acquisition operation and the AD conversion of the high-speed acquisition card, and the temperature information distributed along the optical fiber, namely the temperature-position curve distributed along the optical fiber, is demodulated through the light intensity curves of the stokes light and the anti-stokes light.
Furthermore, the input end of the wavelength division multiplexer is connected with the pulse laser, the public end of the wavelength division multiplexer is connected with the reference optical fiber, two output ends of the wavelength division multiplexer respectively output Stokes light and anti-Stokes light to two input ends of the photoelectric detector, two output ends of the photoelectric detector are connected with the high-speed acquisition card, and the high-speed acquisition card is transmitted to the mainboard through acquisition and conversion and then demodulates temperature information.
Furthermore, the optical switch is a four-channel optical switch, the opening and closing of the four channels are controlled, the common end of the optical switch is connected with the reference optical fiber, and the four channels are respectively connected with the four long-distance sensing optical fibers.
Furthermore, the power supply supplies power to the pulse laser, the optical switch, the photoelectric detector, the high-speed acquisition card and the mainboard.
Further, the reference fiber is a silica fiber having a length of about 150 meters.
The application also discloses a fire alarm method for predicting the temperature of the optical fiber by using the multipoint temperature dispersion coefficient, which comprises the following steps:
the first reference optical fiber is placed in first constant-temperature water bath equipment, and the temperature is set to be T1The second reference optical fiber is placed in a second constant-temperature water bath device, and the temperature is set to be T2；
Starting the distributed fiber Raman temperature measurement system, demodulating temperature information distributed along the fiber by the distributed fiber Raman temperature measurement system through the light intensity curves of Stokes light and anti-Stokes light, and drawing a temperature-position curve;
setting a constant temperature alarm threshold value and a differential temperature alarm threshold value, starting a constant temperature alarm program, a differential temperature alarm program and a temperature prediction program while starting a temperature demodulation program;
if the temperature value of a certain position of the optical fiber is detected to be larger than the constant temperature alarm threshold value, an alarm program is started, an alarm indicator lamp is turned on, and the system positions the alarm position and displays the alarm time;
if the difference value between the current temperature and the previous moment at a certain position of the optical fiber in the continuous time is detected to be greater than the differential temperature alarm threshold value, an alarm program is started, an alarm indicator lamp is turned on, and the system positions the alarm position and displays the alarm time;
temperature prediction procedure: measuring and recording the current time T of the same position of the optical fiber in continuous timenThe previous setting of the secondary temperature data, the current time TnDividing the previously set secondary temperature data into three groups according to the time sequence, averaging the temperature data of each group, if the absolute value of the difference between the temperature average value of the third group and the temperature average value of the second group is larger than the absolute value of the difference between the temperature average value of the third group and the temperature average value of the second group, performing second temperature prediction alarm, otherwise, setting a threshold value of the difference of discrete coefficients, and calculating the current time TnAnd if the absolute value of the difference between the multipoint temperature discrete coefficient at the current moment and the multipoint temperature discrete coefficient at the previous moment in the previously set secondary temperature data is greater than the threshold value of the set discrete coefficient difference, a first temperature prediction alarm is carried out.
Further, the temperature demodulation formula of the distributed fiber raman temperature measurement system is as follows:
wherein
In the formula, PAS、PSRespectively representing the optical power of backward anti-Stokes Raman scattered light and backward Stokes Raman scattered light, upsilon is the propagation speed of light in the optical fiber, and E0H and k are respectively Planck constant and Boltzmann constant, and Delnu is in quartz fiberAmount of raman frequency shift of (f)AS、ΓSScattering coefficients of backward anti-Stokes Raman scattered light and backward Stokes Raman scattered light per unit length in an optical fiber, respectively, α0、αAS、αSLoss coefficients of incident pump light (backward Rayleigh scattered light), backward anti-Stokes Raman scattered light and backward Stokes Raman scattered light in a single unit length of an optical fiber respectively, L is the distance from a certain measuring point on the corresponding optical fiber to a measuring starting point, T is the absolute temperature of the measuring point0Is a certain temperature set.
Further, the current time T is calculatednWhen the absolute value of the difference between the current-time multipoint temperature dispersion coefficient and the previous-time multipoint temperature dispersion coefficient in the previously set secondary temperature data is obtained, the previous-time multipoint temperature dispersion coefficient is the ratio of the standard deviation of the previous-time multipoint temperature to the average value of the previous-time multipoint temperature, and the current-time multipoint temperature dispersion coefficient is added to the current-time temperature T during calculationnRejecting the temperature T at the current momentnAnd in the data of the farthest time, the current-time multipoint temperature dispersion coefficient is the ratio of the standard deviation of the current-time multipoint temperature to the average value of the current-time multipoint temperature.
Further, the differential temperature alarm program: firstly, detecting whether the temperature value meets a first condition, if so, starting to detect a second condition, and if so, alarming by an alarm;
wherein, the condition one: if the change difference value of the current temperature and the previous moment of a certain position of the optical fiber in the continuous time is detected to be larger than the differential temperature alarm threshold value;
and a second condition: calculating the light intensity corresponding to the temperature difference value to obtain PLContinuously recording the light intensity values P of the optical fiber at the same position at the previous moment and the next moment1、P2，Calculating the light intensity difference Pd＝|P1/c1-P2/c2If Pd≥PLWherein c is1，c2Are dynamic coefficients related to the position of the optical fiber at the same position at the previous moment and the next moment respectively.
Further, the discrete coefficient difference threshold is set according to different constant temperature alarm thresholds and combined results of multiple repeated experiments.
Compared with the prior art, the invention has the beneficial effects that:
the invention relates to a method for predicting the temperature of all optical fibers, which is a method for predicting the future temperature change by using the latest obtained temperature data.
Compared with the existing alarm method applied to distributed optical fiber temperature measurement, the method has the advantages that the three temperature alarm methods, namely a constant temperature alarm method, a differential temperature alarm method and a temperature prediction method, operate simultaneously, and a light intensity judgment method is introduced into the differential temperature alarm method, so that the probability of false alarm is effectively reduced compared with the existing alarm method only depending on the temperature change rate; in the prediction method of the optical fiber temperature, the temperature change condition at the future moment is judged and predicted by using the discrete coefficients of the current temperature and the past temperature, so that the alarm response time is effectively reduced.
The differential temperature alarm method introduces light intensity reference to reduce the probability of false alarm; the adoption of the algorithm in the temperature prediction method enables the temperature prediction method to meet the alarm time requirement of the national standard.
The method for detecting the temperature of the multiple points to judge the temperature at the next moment is added, so that whether the alarm is needed or not can be judged in advance without waiting for the time point when the acquisition card acquires and calculates the temperature reaching the threshold temperature.
The method introduces a light intensity judgment method in the differential temperature alarm method, thereby effectively reducing the probability of false alarm; in the method for prejudging the temperature of the optical fiber, the temperature change condition at the future moment is predicted by using the discrete coefficients of the current temperature and the past temperature, so that the alarm response time is effectively reduced.
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The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the application and, together with the description, serve to explain the application and are not intended to limit the application.
FIG. 1 is a structural diagram of a distributed fiber Raman temperature measurement system according to the present invention;
FIG. 2 is a flow chart of a temperature alarm procedure of the distributed fiber Raman temperature measurement system according to the present invention;
in the figure: 1-pulse laser, 2-WDM, 3-reference fiber, 4-optical switch, 5-APD, 6-high speed collection card, 7-mainboard, 8-power.
Detailed Description
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
In an exemplary embodiment of the present application, as shown in fig. 1, there is provided a fire alarm system for predicting a temperature of an optical fiber using a multiple point temperature dispersion coefficient, including: a distributed Raman temperature measurement system comprises a pulse laser (1), a WDM (2), a reference optical fiber (3), an optical switch (4), an APD (avalanche photo diode) (5), a high-speed acquisition card (6), a main board (7), a power supply (8), first constant-temperature water bath equipment, second constant-temperature water bath equipment and a sensing optical fiber.
The pulse laser (1) comprises a pulse generator, a seed source laser, a pump laser, a temperature control module, a WDM1, an erbium-doped fiber, a WDM2 and an optical filter.
The WDM1 and the WDM2 are located inside the pulse laser and are 1x2 WDM; the WDM (2) is located in the system outside the light source and is 1X3 WDM; the wavelengths passed are different.
The input end of the WDM (2) is connected with the pulse laser (1), the common end is connected with the reference optical fiber (3), two output ends respectively output Stokes light and anti-Stokes light to two input ends of the APD (5), two output ends of the APD (5) are connected with the high-speed acquisition card (6), the two output ends are transmitted to the mainboard (7) through acquisition and conversion and then demodulate temperature information
The reference fiber (3) is a quartz fiber with the length of about 150 meters;
the optical switch (4) is a four-channel optical switch, controls the opening and closing of the four channels, the common end is connected with the reference optical fiber (3), and the four channels are respectively connected with the four long-distance sensing optical fibers.
And the power supply (8) supplies power to the pulse laser (1), the optical switch (4), the APD (5), the high-speed acquisition card (6) and the mainboard (7).
In another exemplary embodiment of the present application, a fire alarm method for predicting a temperature of an optical fiber using a multi-point temperature dispersion coefficient is disclosed, which includes:
the method comprises the following steps: based on the built fire alarm system which uses the multipoint temperature discrete coefficient to predict the optical fiber temperature;
step two: two sections of optical fibers with certain lengths are randomly selected from the middle parts of the four sensing optical fibers respectively to serve as a first reference optical fiber and a second reference optical fiber, the first reference optical fiber is placed in a first constant-temperature water bath device, the temperature is set to be 20 ℃, the second reference optical fiber is placed in a second constant-temperature water bath device, the temperature is set to be 20 ℃, 30 ℃, 40 ℃, 50 ℃, 60 ℃, 70 ℃, 80 ℃, 84 ℃, 91 ℃ and 98 ℃ respectively at different time (the filling liquid in the constant-temperature water bath is edible oil).
Step three: as shown in fig. 2, the distributed fiber raman temperature measurement system is started, pulsed light emitted by a pulse laser enters a reference fiber through a WDM, and then enters a sensing fiber through a light switch, the pulsed light generates backward scattered light at each point inside the reference fiber and the sensing fiber, wherein backward stokes light and backward anti-stokes light enter an APD through two output ends of the WDM, and then light intensity curves of the stokes light and the anti-stokes light are obtained through acquisition operation and AD conversion by a high-speed acquisition card;
step four: the Raman temperature measurement system demodulates temperature information distributed along the optical fiber through light intensity curves of Stokes light and anti-Stokes light and draws a temperature-position curve;
the specific temperature demodulation formula is as follows:
wherein
In the formula, PAS、PSRespectively representing the optical power of backward anti-Stokes Raman scattered light and backward Stokes Raman scattered light, upsilon is the propagation speed of light in the optical fiber, and E0H and k are respectively Planck constant and Boltzmann constant, Delnu is Raman frequency shift quantity in quartz optical fiber, and gamma is energy of pumping light pulseAS、ΓSScattering coefficients of backward anti-Stokes Raman scattered light and backward Stokes Raman scattered light per unit length in an optical fiber, respectively, α0、αAS、αSLoss coefficients of incident pump light (backward Rayleigh scattered light), backward anti-Stokes Raman scattered light and backward Stokes Raman scattered light in a single unit length of an optical fiber respectively, L is the distance from a certain measuring point on the corresponding optical fiber to a measuring starting point, T is the absolute temperature of the measuring point0Is a certain temperature set.
The experiment is divided into 10 groups of experiments according to the temperature difference of the second constant-temperature water bath equipment, and the temperature of the second constant-temperature water bath equipment is respectively 20 ℃, 30 ℃, 40 ℃, 50 ℃, 60 ℃, 70 ℃, 80 ℃, 84 ℃, 91 ℃ and 98 ℃.
Setting the system operating temperature to Ta. Differential temperature alarmAlarm threshold is Tb；
And (4) a temperature setting alarm program: taking the temperature of the second constant-temperature water bath equipment as an example of 84 ℃, if the temperature value of a certain position of the current optical fiber is demodulated to be more than 60 ℃, an alarm program is started, an alarm indicator lamp is turned on, and the system displays alarm time and an alarm position;
and (3) a differential temperature alarm program: the first condition is as follows: if the difference value of the current temperature of a certain position of the optical fiber and the change of the previous moment in the continuous time is detected to be greater than Tb(ii) a And a second condition: calculating the temperature difference TbThe corresponding light intensity is obtained as PLContinuously recording the light intensity values P of the optical fiber at the same position at the previous moment and the next moment1、P2Calculating the light intensity difference Pd＝|P1/c1-P2/c2If Pd≥PLWherein c is1，c2Are dynamic coefficients related to the position of the optical fiber at the same position at the previous moment and the next moment respectively.
Firstly, detecting whether the temperature value meets a first condition, if so, starting to detect a second condition, and if so, entering a second differential temperature alarm program and giving an alarm by an alarm;
temperature prediction procedure: measuring and recording the current time T of the same position of the optical fiber in continuous timenThe first 15 times of temperature data, recorded as Tn-15,Tn-14,Tn-13,...,Tn-2,Tn-1；
Calculating Tn1＝(Tn-11+Tn-12+Tn-13+Tn-14+Tn-15)/5，
Tn2＝(Tn-6+Tn-7+Tn-8+Tn-9+Tn-10)/5，
Tn3＝(Tn-1+Tn-2+Tn-3+Tn-4+Tn-5)/5；
Compare T in sequencen1，Tn2，Tn3If | T is satisfiedn3-Tn2|≥|Tn2-Tn1If yes, entering a temperature prediction program II: starting an alarm program, turning on an alarm indicator light and positioning a systemAlarming position and displaying alarming time; otherwise, entering a first prediction program: according to a constant temperature alarm threshold T1Setting the threshold value of the discrete coefficient difference as cv，
Calculating Tn-15,Tn-14,Tn-13,...,Tn-2,Tn-1The discrete coefficient of the 15 points is calculated by the method cv1＝σ1/μ1，
Wherein mu1＝(Tn-15+Tn-14+Tn-13+...+Tn-2+Tn-1)/15，
Adding the temperature T at the current momentnRemoving Tn-15Calculating Tn-14，Tn-13，...，Tn-2，Tn-1，TnThe discrete coefficient of the 15 points is calculated by the method cv2＝σ2/μ2，
Wherein mu2＝(Tn-14+Tn-13+...+Tn-2+Tn-1+Tn)/15，
ComputingΔcv＝|cv1-cv2If at allΔcv＞cv,
Then an alarm program is started, an alarm indicator lamp is on, and the system positions an alarm position and displays alarm time.
Wherein c isvThe method is set according to the results of setting different constant temperature alarm thresholds, combining temperature alarm and discrete coefficient correlation theory and multiple repeatability experiments.
And after the alarm is finished, restarting the temperature demodulation program and the temperature alarm program, and restarting the temperature demodulation and the temperature prejudgment.
The distributed optical fiber temperature measurement system is used for collecting the light intensity values of Anti-Stokes light and Stokes light at each point of the optical fiber and the corresponding demodulated temperature value, processing the collected light intensity and temperature value, and comparing the temperature and light intensity with an alarm threshold value to determine whether a differential temperature or constant temperature alarm condition is met; meanwhile, the temperature at the next moment is predicted by using the current temperature value and the discrete coefficients of the temperatures at a plurality of past points, and whether an alarm is needed or not is judged; if the alarm condition is met, the alarm position is positioned, and the alarm time is displayed. The method introduces a light intensity judgment method in the differential temperature alarm method, thereby effectively reducing the probability of false alarm; in the method for prejudging the temperature of the optical fiber, the temperature change condition at the future moment is predicted by using the discrete coefficients of the current temperature and the past temperature, so that the alarm response time is effectively reduced.
Compared with the prior art, the algorithm can perform temperature early warning more quickly under the same hardware condition; according to the regulation of GB-16280-2014, under the conditions that the initial temperature is 25 +/-2 ℃ (the initial temperature is not less than 138 ℃ for the set action temperature, 50 +/-2 ℃) and the airflow rate is 0.8m/s +/-0.1 m/s, the temperature of a sensitive part with the standard alarm length at any section of the detector is increased at the temperature increase rate of 1 ℃/min, and the corresponding time of the constant temperature detector and the difference constant temperature detector is satisfied: t is more than or equal to 60 ℃ and less than or equal to 85 ℃, and the alarm time is not more than 15 seconds.
In the method, the threshold values of the discrete coefficients corresponding to different action temperatures are determined through a plurality of repeated experiments, whether alarm is needed or not can be accurately judged according to the discrete coefficient change of the first 2 to 3 points when the temperature changes, and the method has obvious advantages in fire alarm compared with the existing method.
The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.
Claims (9)
1. A fire alarm system for predicting the temperature of an optical fiber by using multipoint temperature discrete coefficients is characterized by comprising the following components: a distributed optical fiber Raman temperature measuring system is provided,
collecting light intensity values of Stokes light and anti-Stokes light of each point of the optical fiber and corresponding demodulated temperature values through a distributed optical fiber temperature measuring system, processing the collected light intensity and temperature values, and comparing the temperature and light intensity with an alarm threshold value to determine whether a differential temperature or constant temperature alarm condition is met;
during temperature prediction, the current time T of the same position of the optical fiber is measured and recorded in continuous timenThe previous setting of the secondary temperature data, the current time TnDividing the previously set secondary temperature data into three groups according to the time sequence, averaging the temperature data of each group, if the absolute value of the difference between the temperature average value of the third group and the temperature average value of the second group is larger than the absolute value of the difference between the temperature average value of the second group and the temperature average value of the first group, performing second temperature prediction alarm, otherwise, setting a threshold value of the difference of discrete coefficients, and calculating the current time TnIf the absolute value of the difference between the multipoint temperature discrete coefficient at the current moment and the multipoint temperature discrete coefficient at the previous moment in the previously set secondary temperature data is greater than the threshold value of the set discrete coefficient difference, a first temperature prediction alarm is carried out;
and (3) a differential temperature alarm program: firstly, detecting whether the temperature value meets a first condition, if so, starting to detect a second condition, and if so, alarming by an alarm;
wherein, the difference temperature alarm program: the first condition is as follows: if the difference value of the current temperature of a certain position of the optical fiber and the change of the previous moment in the continuous time is detected to be greater than Tb(ii) a And a second condition: calculating the temperature difference TbThe corresponding light intensity is obtained as PLContinuously recording the light intensity values P of the optical fiber at the same position at the previous moment and the next moment1、P2Calculating the light intensity difference Pd＝|P1/c1-P2/c2If Pd≥PLWherein c is1，c2Are dynamic coefficients related to the position of the optical fiber at the same position at the previous moment and the next moment respectively.
2. The fire alarm system using the multipoint temperature dispersion coefficient to predict the temperature of the optical fiber according to claim 1, wherein the distributed fiber Raman temperature measurement system comprises a pulse laser, and pulse light emitted by the pulse laser enters the reference optical fiber through a wavelength division multiplexer and then enters the sensing optical fiber through an optical switch;
the middle part of each sensing optical fiber is respectively and randomly selected to be used as a first reference optical fiber and a second reference optical fiber with a certain length, and the two optical fibers are respectively placed in the respective corresponding constant-temperature water bath equipment.
3. The fire alarm system using the multi-point temperature dispersion coefficient to predict the fiber temperature according to claim 2, wherein the pulse light generates backward scattered light at each point inside the reference fiber and the sensing fiber, wherein the backward stokes light and the backward anti-stokes light enter the photoelectric detector through two output ends of the wavelength division multiplexer, then the light intensity curves of the stokes light and the anti-stokes light are obtained through the acquisition operation and the AD conversion of the high-speed acquisition card, and the temperature information distributed along the fiber, that is, the temperature-position curve distributed along the fiber is demodulated through the light intensity curves of the stokes light and the anti-stokes light.
4. The fire alarm system according to claim 2, wherein the input terminal of the wavelength division multiplexer is connected to the pulse laser, the common terminal of the wavelength division multiplexer is connected to the reference fiber, two output terminals of the wavelength division multiplexer respectively output stokes light and anti-stokes light to two input terminals of the photodetector, and two output terminals of the photodetector are connected to the high-speed acquisition card and transmitted to the main board through acquisition and conversion to demodulate the temperature information.
5. The fire alarm system according to claim 2, wherein the optical switch is a four-channel optical switch for controlling the opening and closing of four channels, the common end of the optical switch is connected to the reference optical fiber, and the four channels are respectively connected to the four long-distance sensing optical fibers.
6. The fire alarm method for predicting the optical fiber temperature by using the multipoint temperature discrete coefficient is characterized by comprising the following steps:
the first reference optical fiber is placed in first constant-temperature water bath equipment, and the temperature is set to be T1The second reference optical fiber is placed in a second constant-temperature water bath device, and the temperature is set to be T2；
Starting the distributed fiber Raman temperature measurement system, demodulating temperature information distributed along the fiber by the distributed fiber Raman temperature measurement system through the light intensity curves of Stokes light and anti-Stokes light, and drawing a temperature-position curve;
setting a constant temperature alarm threshold value and a differential temperature alarm threshold value, starting a constant temperature alarm program, a differential temperature alarm program and a temperature prediction program while starting a temperature demodulation program;
if the temperature value of a certain position of the optical fiber is detected to be larger than the constant temperature alarm threshold value, an alarm program is started, an alarm indicator lamp is turned on, and the system positions the alarm position and displays the alarm time;
if the difference value between the current temperature and the previous moment at a certain position of the optical fiber in the continuous time is detected to be greater than the differential temperature alarm threshold value, an alarm program is started, an alarm indicator lamp is turned on, and the system positions the alarm position and displays the alarm time;
temperature prediction procedure: measuring and recording the current time T of the same position of the optical fiber in continuous timenThe previous setting of the secondary temperature data, the current time TnDividing the previously set secondary temperature data into three groups according to the time sequence, averaging the temperature data of each group, if the absolute value of the difference between the temperature average value of the third group and the temperature average value of the second group is larger than the absolute value of the difference between the temperature average value of the second group and the temperature average value of the first group, performing second temperature prediction alarm, otherwise, setting a threshold value of the difference of discrete coefficients, and calculating the current time TnThe absolute value of the difference between the multipoint temperature dispersion coefficient at the current time and the multipoint temperature dispersion coefficient at the previous time in the previously set secondary temperature data is larger than the threshold of the set dispersion coefficient difference, and then the first temperature is carried outPredicting and alarming;
wherein, the difference temperature alarm program: firstly, detecting whether the temperature value meets a first condition, if so, starting to detect a second condition, and if so, alarming by an alarm;
wherein, the condition one: if the change difference value of the current temperature and the previous moment of a certain position of the optical fiber in the continuous time is detected to be larger than the differential temperature alarm threshold value;
and a second condition: calculating the light intensity corresponding to the temperature difference value to obtain PLContinuously recording the light intensity values P of the optical fiber at the same position at the previous moment and the next moment1、P2Calculating the light intensity difference Pd＝|P1/c1-P2/c2If Pd≥PLWherein c is1，c2Are dynamic coefficients related to the position of the optical fiber at the same position at the previous moment and the next moment respectively.
7. The method of claim 6, wherein the distributed fiber Raman temperature measurement system has a temperature demodulation formula as follows:
wherein
In the formula, PAS、PSRespectively representing the optical power of backward anti-Stokes Raman scattered light and backward Stokes Raman scattered light, upsilon is the propagation speed of light in the optical fiber, and E0H and k are respectively Planck constant and Boltzmann constant, Delnu is Raman frequency shift quantity in quartz optical fiber, and gamma is energy of pumping light pulseAS、ΓSScattering coefficients of backward anti-Stokes Raman scattered light and backward Stokes Raman scattered light per unit length in an optical fiber, respectively, α0、αAS、αSRespectively are loss coefficients of incident pump light, backward anti-Stokes Raman scattered light and backward Stokes Raman scattered light in a single unit length of an optical fiber, L is the distance from a certain measuring point on the corresponding optical fiber to a measuring starting point, T is the absolute temperature of the measuring point, and0is a certain temperature set.
8. The fire alarm method of claim 6, wherein the current time T is calculatednWhen the absolute value of the difference between the current-time multipoint temperature dispersion coefficient and the previous-time multipoint temperature dispersion coefficient in the previously set secondary temperature data is obtained, the previous-time multipoint temperature dispersion coefficient is the ratio of the standard deviation of the previous-time multipoint temperature to the average value of the previous-time multipoint temperature, and the current-time multipoint temperature dispersion coefficient is added to the current-time temperature T during calculationnRejecting the temperature T at the current momentnAnd in the data of the farthest time, the current-time multipoint temperature dispersion coefficient is the ratio of the standard deviation of the current-time multipoint temperature to the average value of the current-time multipoint temperature.
9. The method of claim 6, wherein the discrete coefficient difference threshold c is a multiple of the discrete coefficient difference threshold cvThe method is set according to the result of setting different constant temperature alarm thresholds and combining multiple repeated experiments.
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